It's a performance trade off, because in general it's hard for the compiler to know whether it needs to insert a memory barrier or not if you do something like:

It's a performance trade off, because in general it's hard for the compiler to know whether it needs to insert a memory barrier or not if you do something like: this.fooField = new Something() which would need a memory barrier if another thread is expected to access fooField concurrently, and not need one otherwise. Putting memory barriers on every field assignment of a constructed object would be pretty expensive. It's also worth noting there's not anything that special about constructors here; there's a million other ways you can get similar issues when you try to handle concurrency at this level. For example if you do: this.bar.changeSomeFields() this.fooField = this.bar and changeSomeFields doesn't invoke a memory barrier at the right time you'll get the same problem if fooField isn't volatile.